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A309812 Odd integers k such that k^2 is arithmetic mean of two other perfect squares. 1
5, 13, 15, 17, 25, 29, 35, 37, 39, 41, 45, 51, 53, 55, 61, 65, 73, 75, 85, 87, 89, 91, 95, 97, 101, 105, 109, 111, 113, 115, 117, 119, 123, 125, 135, 137, 143, 145, 149, 153, 155, 157, 159, 165, 169, 173, 175, 181, 183, 185, 187, 193, 195, 197, 203, 205, 215, 219 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..58.

EXAMPLE

5 is a term because 5^2 = 25 = (1^2 + 7^2)/2.

MATHEMATICA

Select[Range[1, 300, 2], SquaresR[2, 2 #^2] > 4 &] (* Giovanni Resta, Aug 18 2019 *)

PROG

(PARI) isok(n) = {if (n %2, for (i=1, n, x = 2*n^2-i^2; if ((x!=i^2) && (x>0) && issquare(x), return (i)); ); ); } \\ Michel Marcus, Aug 18 2019

CROSSREFS

Intersection of A005408 and A009003.

Sequence in context: A090759 A090758 A327922 * A324909 A322105 A230503

Adjacent sequences:  A309809 A309810 A309811 * A309813 A309814 A309815

KEYWORD

nonn

AUTHOR

Mohsin A. Shaikh, Aug 18 2019

EXTENSIONS

More terms from Giovanni Resta, Aug 18 2019

STATUS

approved

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Last modified January 28 07:07 EST 2020. Contains 331317 sequences. (Running on oeis4.)